1. Field of the Invention
The present invention relates generally to an improved lathe spindle assembly for mounting a workpiece for rotation during a machining operation, and it relates more particularly to a new and improved lathe spindle assembly having the capability of self-adjusting to differing geometric tolerances of a plurality of interchangeable workpiece arbors.
2. Description of the Prior Art
A typical lathe of the general type to which the present invention relates is disclosed, for example, in U.S. Pat. No. 2,891,435 issued to H. R. Billeter, dated June 23, 1959. The aforesaid patent discloses a lathe in which a generally cylindrical spindle is rotated about its longitudinal axis and supports a workpiece during a process of machining. Such a lathe is especially well suited for the machining of automotive brake drums or rotors mounted to an arbor inserted within the lathe spindle.
In order to provide a lathe having the advantage of versatility in the machining of workpieces, it is known to construct a lathe spindle which is capable of receiving a plurality of workpiece arbors which, in turn, are specially adapted for connection to drums or rotors of various sizes and configurations. Typically, the arbors are generally elongate members having a forward end for connection to the workpiece and a rearward end which is insertable into a bore within the driven spindle of the lathe. The rearward end of the arbor is formed with a first annular tapered surface and a second annular tapered surface is formed on the arbor at a position intermediate the forward and rearward ends thereof. These surfaces are cooperable with corresponding tapered surfaces, respectively machined on the interior wall of the spindle bore. A draw bar which is threadedly received by the rearward end of each arbor is then used to draw the arbor interiorly of the driven spindle whereupon the arbor is fixedly retained within the spindle.
A disadvantage of the lathe spindle assembly of the foregoing type is that critical tolerances must be held in the machining of the tapered surfaces of the arbor and driven spindle in order to support the arbor for concentric rotation with the spindle. These critical tolerances are essential for purposes of supporting the workpiece for rotation without runout, which would cause the workpiece to rotate eccentrically thereby rendering it impossible to properly machine the workpiece surfaces. In addition, particularly where multiple spindles are used to add versatility to the lathe functions, the requirement of holding close tolerances in the fabrication of the lathe arbors adds considerably to the cost of the lathe assembly.
To overcome the foregoing disadvantages of the prior art, a lathe spindle assembly of the present invention comprises a generally cylindrical body having a forward end and a rearward end and an internal bore extending longitudinally thereof. An arbor having a forward end and a rearward end is insertable into the bore of the spindle body and carries a workpiece on the forward end thereof. The rearward end of the arbor is provided with a first annular tapered surface formed thereon. Correspondingly, a second annular tapered surface is formed on the arbor at an intermediate position between the forward and rearward ends thereof. An interior annular tapered surface is formed at the forward end of the spindle body and is configured to seat against the second annular tapered surface of the arbor. In addition, a collar member is insertable within the bore of the spindle body and is formed with an interior tapered surface configured to seat against the first annular tapered surface of the arbor. A draw bar extends through the bore of the spindle body and is threadedly received by the rearward end of the arbor for drawing the arbor interiorly of the spindle body. Means associated with the draw bar are provided for drawing the arbor interiorly of the spindle body. The assembly is further provided with means for biasing the collar member into engagement with the arbor whereupon the first annular tapered surface of the arbor seats against the interior annular tapered surface of the collar, and the second annular tapered surface of the arbor seats against the interior annular tapered surface of the spindle body. By such an arrangement, the tapered surfaces of both the spindle body and the arbor may be formed without adherence to close tolerances because the biasing means within the spindle body compresses the collar member against the arbor despite variations in the actual dimensions and longitudinal positions of the tapered surfaces of the arbor.